The present invention relates to method and apparatus for automatic running control of a loom, and more particularly relates to an improvement in an automatic system for controlling the level of electric voltage to be applied to a drive motor for a loom during the starting period of loom running and at transit to normal running.
For various reasons, the level of electric voltage to be applied to a drive motor has to be time-functionally controlled properly in particular during the starting period of loom running. Such voltage level control is necessitated mainly from the viewpoint of stripe defect protection. The stripe defects herein referred to includes thick and thin places extending in the weft direction of a woven fabric. Such stripe defects are in general generated by improper beating on the cloth-fell.
First, such improper beating is resulted from the state of yarns during stoppage of the loom. When the loom is at stoppage, condition of the yarns is quite different from that during normal running because of slack or tension appearing on the yarns. When running of the loom is started and directly brought to normal running condition, a stripe defect is generated on the fabric at the startng position. The type of stripe defect of this sort varies from fabric to fabric. When some slack appears on the yarns during stoppage of the loom, torque provided ordinarily by the drive motor at starting is in general too small to assure sufficient beating on the cloth-fell and, as a consequence, a thin place is developed on the fabric. When some tension appears on the yarns during stoppage of the loom, torque provided ordinarily by the drive motor at starting is in general too large to assure moderate beating on the cloth-fell and, as a consequence, a thick place is developed on the fabric.
Second, such improper beating is resulted from the starting characteristics of the drive motor itself. For provision of large torque at starting of loom running, use of a motor with large starting torque such as a double squirrel cage induction motor is generally employed. Use of such a drive motor indeed assure proper beating motion during the starting period of loom running on the one hand. A drive motor of this type, however, is on the other hand very poor in its running characteristics during normal running period of the loom and, as a consequence, requires increased power consumption with low efficienty. Recent trend for higher speed running of a loom furthers the need for use of a drive motor providable of larger starting torque.
It is well known by ones skilled in the art that an electric device generally exhibits the highest efficiency when driven for operation under application of its rated voltage which also causes minimum operational troubles. Thus, continuous application of a voltage higher than the rated voltage to a drive motor tends to lower the efficiency and cause operational troubles such as burning of its windings.
In order to avoid such inconveniency, it was already proposed by the inventors of the present invention to limit application of such a higher voltage to the starting period of loom running only and to change the voltage to the rated voltage after the starting period. This proposal well suffices both the requirements for large torque during the starting period and the requirement for higher efficiency during the normal running period.
At transit from the higher voltage to the rated voltage, momentary disappearance of voltage acting on the drive motor occurs unavoidably. If such disappearance of voltage takes place at the very moment of beating on the cloth-fell, fall in torque provided by the drive motor develops thin place on the fabric.